What problem arise when segregation dominates a city, states, and country.

You are asking quite a few questions here. Slavery has taken place throughout history and goes on to this day. People who are taken advantage of with little to no compensation and forced to do things that they do not want to is pretty much slavery. Segregation would have been the norm during the time of To kill a Mockingbird. The separation of blacks and whites permeated society. Racism was accepted and the result was a very fractured nation. There was no harmony with segregation, only hate and humiliation. With segregation a country slowly dies. Whether South Africa or the United states, people fractured by ignorance lead only to political and cultural strife. The ideology behind it is what lead to Tom Robinson's tragic story in Mockingbird.